Argon tagging of doubly transition metal doped aluminum clusters: The importance of electronic shielding

The interaction of argon with doubly transition metal doped aluminum clusters, AlnTM2+ (n = 1–18, TM = V, Nb, Co, Rh), is studied experimentally in the gas phase via mass spectrometry. Density functional theory calculations on selected sizes are used to understand the argon affinity of the clusters, which differ depending on the transition metal dopant. The analysis is focused on two pairs of consecutive sizes: Al6,7V2+ and Al4,5Rh2+, the largest of each pair showing a low affinity toward Ar. Another remarkable observation is a pronounced drop in reactivity at n = 14, independent of the dopant element. Analysis of the cluster orbitals shows that this feature is not a consequence of cage formation but is electronic in nature. The mass spectra demonstrate a high similarity between the size-dependent reactivity of the clusters with Ar and H2. Orbital interactions provide an intuitive link between the two and further establish the importance of precursor states in the reactions of the clusters with hydrogen

An octacoordinated Nb atom in the NbAl₈H₈⁺ cluster

The NbAl8H8+ cluster was formed in a molecular beam and characterized by mass spectrometry and infrared spectroscopy. Density functional theory calculations show the lowest-energy isomer is a high symmetry singlet with the Nb atom placed at the center of a distorted hexagonal Al ring and coordinated by two AlH moieties, therefore exhibiting octacoordination. The unprecedented high-symmetric geometry is attributed to the 20 valence electrons; the central Nb atom adheres to the 18-electron rule and two additional delocalized electrons stabilize the hexagonal ring

Altering CO binding on gold cluster cations by Pd-doping

The introduction of dopant atoms into metal nanoparticles is an effective way to control the interaction with adsorbate molecules and is important in many catalytic processes. In this work, experimental and theoretical evidence of the influence of Pd doping on the bonding between small cationic AuN+ clusters and CO is presented. The CO adsorption is studied by combining low-pressure collision cell reactivity and infrared multiple photon dissociation spectroscopy experiments with density functional theory calculations. Measured dissociation rates of cluster–CO complexes (N≤21) allow the estimation of cluster–CO binding energies, showing that Pd doping increases the CO adsorption energy to an extent that is size-dependent. These trends are reproduced by theoretical calculations up to N= 13. In agreement with theory, measurements of the C–O vibrational frequency suggest that for the doped PdAuN-1+ (N=3–5, 11) clusters, CO adsorbs on an Au atom, while for N=6–10 and N=12–14, CO interacts directly with the Pd dopant. A pronounced red-shifting of the C–O vibrational frequency is observed when CO interacts directly with the Pd dopant, indicating a significant back-donation of electron charge from Pd to CO. In contrast, the blue-shifted frequencies, observed when CO interacts with an Au atom, indicate that σ-donation dominates the Au–CO interaction. Studying such systems at the sub-nanometre scale enables a fundamental comprehension of the interactions between adsorbates, dopants and the host (Au) species at the atomic level

Reactivity of Cobalt-Fullerene Complexes towards Deuterium

The adsorption of molecular deuterium (D2) onto charged cobalt-fullerene-complexes ConC60 + (n=1–8) is measured experimentally in a few-collision reaction cell. The reactivity is strongly size-dependent, hinting at clustering of the transition metal atoms on the fullerenes. Formation and desorption rate constants are obtained from the pressure-dependent deuterogenation curves. DFT calculations indeed find that this transition metal clustering is energetically more favorable than decorating the fullerene. For n=1, D2 is predicted to bind molecularly and for n=2 dissociative and molecular configurations are quasi-isoenergetic. For n=3–8, dissociation of D2 is thermodynamically preferred. However, reaching the ground state configuration with dissociated deuterium on the timescale of the experiment may be hindered by dissociation barriers.Fil: Vanbuel, Jan. Katholikie Universiteit Leuven; BélgicaFil: German, Estefania. Universidad de Valladolid; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Libeert, Guillaume. Katholikie Universiteit Leuven; BélgicaFil: Veys, Koen. Katholikie Universiteit Leuven; BélgicaFil: Moens, Janni. Katholikie Universiteit Leuven; BélgicaFil: Alonso, Julio A.. Donostia International Physics Center; España. Universidad de Valladolid; EspañaFil: López, María J.. Universidad de Valladolid; EspañaFil: Janssens, Ewald. Katholikie Universiteit Leuven; Bélgic

Effects of Charge Transfer on the Adsorption of CO on Small Molybdenum-Doped Platinum Clusters

The interaction of carbon monoxide with platinum alloy nanoparticles is an important problem in the context of fuel cell catalysis. In this work, molybdenum-doped platinum clusters have been studied in the gas phase to obtain a better understanding of the fundamental nature of the Pt–CO interaction in the presence of a dopant atom. For this purpose, Ptn+ and MoPtn-1+ (n=3–7) clusters were studied by combined mass spectrometry and density functional theory calculations, making it possible to investigate the effects of molybdenum doping on the reactivity of platinum clusters with CO. In addition, IR photodissociation spectroscopy was used to measure the stretching frequency of CO molecules adsorbed on Ptn+ and MoPtn-1+ (n=3–14), allowing an investigation of dopant-induced charge redistribution within the clusters. This electronic charge transfer is correlated with the observed changes in reactivity

Towards a learning organisation

As we face a revolutionary move towards e-learning and away from traditional face-to-face training, today's human resource manager implementing technology-supported training needs a concise, practical handbook outlining the choices that have to be made and the implications of each approach. 'Towards a learning organisation' brings human resource managers up-to-date with the various applications that are open to them, such as Electronic Learning Environments, Web based training, Videoconferencing, etc. This handbook provides user-friendly information about emerging technologies for training, checklists and other decision-making tools. Based on broad experience and peppered throughout with case studies and examples from leading European companies and institutions, it also offers plenty of background information including an onverview of network options as well as a handy glossary and further resources list

Effect of radiative cooling on the size-dependent stability of small boron clusters

The mass spectrum of cationic boron clusters, BN+ (N = 5 − 20), after photoexcitation demonstrates that radiative cooling is an important, though often neglected, process in determining the relative stability of small and isolatedparticles. The observed intensities in massspectra suggest that B5+, B11+, B13+, and B15+ are particularly stable clusters, consistent with density-functional theory calculations. Quantitative agreement, however, is only obtained if radiative cooling is included in the analysis. All clusters are found to radiate on microsecond timescales, suggesting recurrent fluorescence as the dominant photon emission process

The redox environment differentially regulates autophagy in leaves and roots of Arabidopsis thaliana during cadmium stress

Resumen del poster presentado en: Redox Biology Congress. Gante, Bélgica; 24-26 de agosto (2022

Hydrogen Adsorption and Dissociation on Al_nRh₂⁺ (n=1 to 9) Clusters: Steric and Coordination Effects

The interaction of molecular hydrogen with doubly rhodium doped aluminum clusters, AlnRh2+ (n = 1 to 9), is investigated by a combination of time-of-flight mass spectrometry, infrared multiple photon dissociation spectroscopy, and density functional theory calculations. The reactivity of the AlnRh2+ clusters toward H2 is found to be sensitive to cluster size, with sizes n = 1 to 4 and 7 being the most reactive. Al3Rh2+ and Al4Rh2+ are the only species that thermodynamically prefer molecular over dissociative H2 adsorption. Calculated molecular adsorption energies of a single H2 molecule correlate well with the experimental abundances of the hydrogenated species, and the potential energy profiles reveal that H2 dissociation only has submerged barriers for n = 1, 2, and 7. In contrast, the molecularly hydrogenated complexes seem to be kinetically trapped for n = 5, 6, 8, and 9 due to significant energy barriers. This indicates that the initial molecular H2 adsorption on the Rh atoms and thereafter dissociation are the determining steps for the hydrogenation reaction. An analysis of the cluster geometries reveals that the coordination environment and the steric factor of the Rh atoms are the main descriptors for the size-dependent reactivity of the AlnRh2+ clusters